Modal testing for model validation of structures with discrete nonlinearities.

Model validation using data from modal tests is now widely practiced in many industries for advanced structural dynamic design analysis, especially where structural integrity is a primary requirement. These industries tend to demand highly efficient designs for their critical structures which, as a result, are increasingly operating in regimes where traditional linearity assumptions are no longer adequate. In particular, many modern structures are found to contain localized areas, often around joints or boundaries, where the actual mechanical behaviour is far from linear. Such structures need to have appropriate representation of these nonlinear features incorporated into the otherwise largely linear models that are used for design and operation. This paper proposes an approach to this task which is an extension of existing linear techniques, especially in the testing phase, involving only just as much nonlinear analysis as is necessary to construct a model which is good enough, or 'valid': i.e. capable of predicting the nonlinear response behaviour of the structure under all in-service operating and test conditions with a prescribed accuracy. A short-list of methods described in the recent literature categorized using our framework is given, which identifies those areas in which further development is most urgently required.

Motor asymmetry and estimation of body-scaled aperture width in Parkinson's disease.

The present study examined how asymmetrical motor symptomatology helps predict the pattern of perceptual judgements of body-scaled aperture width in lateralised Parkinson's disease (PD). Eleven patients with PD predominantly affecting the left side of their body (LPD), 16 patients with PD predominantly affecting their right side (RPD), and 16 healthy controls made forced-choice judgements about whether or not they would fit without turning their shoulders through a life-sized schematic doorway shown on a large screen. Whereas control and LPD groups made accurate estimations of body-scaled aperture width, RPD patients significantly underestimated aperture width relative to their body, perceiving doorways on average that were 12% narrower than their bodies as wide enough to allow them to pass through without rotation. Across all patients, estimates of body-scaled aperture width correlated with ratio of right-to-left symptom severity. These perceptual errors may indicate a mismatch between the neural representation of external space and that of body size in PD.

Effect of a pathway bundle on length of stay.

BACKGROUND: Pathways to guide clinical care are well accepted and used in many emergency departments. We wanted to introduce a number ("bundle") over a short space of time and involve the whole patient stay in the pathway. It was hypothesised that a more efficient process would result with an overall reduction in length of stay (LoS). METHODS: A "bundle" of 14 evidence-based pathways of care was introduced into a medium-sized district general hospital (DGH) in late 2006/early 2007. These pathways covered emergency department care and acute medical care for a period of up to 48 h. A total of 8184 acute emergency admission episodes were audited, 3852 in the 8 months before introduction of the new pathways and 4332 in the 8 months after their introduction. RESULTS: The overall effect of introducing the pathway bundle had a trend towards reduction in LoS by 0.2 days (95% CI -0.2 to 0.5), but this was not statistically significant (p>0.1). However, in those patients with

Natural frequency analysis of osseointegration for trans-femoral implant.

Osseointegration trans-femoral implants are a new orthopaedic anchoring method to attach prosthetic limbs. The clinical success of this promising technique depends on the effectiveness of osseointegration achieved after implantation. The aim of this study is to use the resonant characteristics of the implant system to determine the changes in stability as a reflection of boundary condition of the implant. With a small mechanical excitation, Vibration responses of the trans-femoral implant to a small mechanical excitation were measured using an accelerometer and the vibration signal was analyzed using Fast Fourier Transform (FFT) software to obtain the fundamental natural frequency (NF) of the implant system. In-vitro study was conducted using different silicone rubbers to simulate the interface condition. The result showed that a high NF corresponded to a high elastic modulus of the interface material between the implant and bone. A preliminary in-vivo study with one osseointegration trans-femoral implant patient showed that there was a decrease of NF after initial weight bearing rehabilitation. After continued weight bearing, the NF gradually returned to the pre-loading level at around day 24 and the general trend of the NF reached a stable state 38 days after the first weight bearing exercise.

The incidence and occupational outcome of overuse anterior knee pain during army recruit training.

OBJECTIVES: To determine the incidence and occupational outcome of overuse anterior knee pain (AKP) in Army recruits undergoing basic training. METHODS: A prospective cohort study of 1008 Army recruits. Recruits underwent the 12-week phase 1 training program. Cases of AKP were captured through self-presentation of pain at a primary care medical centre. All recruits medical records were reviewed on leaving training and any other lower limb injuries were recorded for comparison with the AKP group. Training outcomes in terms of medical discharges (MD) and discharges as of right (DAOR) i.e, voluntary discharge, were recorded along with training days lost (TDL) and whether a recruit had been held back in training (BS). RESULTS: 8.75% (95% CI: 6.93-10.57) of recruits reported to the medical centre with AKP. Of these more than half were referred to see a GP and the majority were from patients with no previous history of AKP (91%, 95% CI: 85.2-97.5). The median TDL per AKP case was 3 days (IQR: 3-5 days). The AKP group had a significantly higher (p < 0.01) MD rate (12.5%) than the lower limb injury group (3.3%; 95% CI diff: 1.1-17.2%) and the baseline rate of all other recruits (2.5%; 95% CI diff: 2.3-17.7%). The majority of AKP cases occurred by week 4 (median) of training (IQR: 2.2-64). CONCLUSIONS: There was a high incidence of AKP, and while the short term prognosis appears relatively good in the majority of cases as reflected in the median TDL, a large minority were medically discharged and held back in training. Further work should examine methods of reducing the disease burden of AKP in the Army, addressing areas such as aetiology, prevention and treatment.

An unusual cause of diabetic ketoacidosis and fulminant septicaemia.

BACKGROUND: Diabetic ketoacidosis (DKA) is a common medical emergency. Resistant and recurrent DKA can be due to underlying infection, and a detailed travel history may be important in determining the cause in such cases. We report here a case of unusual DKA and fulminant septicaemia in a Caucasian male with Type 1 diabetes 2 years after returning from living in Thailand. CASE REPORT: A 39-year-old Caucasian male was diagnosed with Type 1 diabetes whilst working in Thailand where he also subsequently developed a cavitating lung lesion diagnosed locally as pulmonary tuberculosis. Two years after returning to the UK he was admitted with DKA and septicaemia. Despite correction of his DKA his condition deteriorated and he developed a fluid collection anterior to the left hip on computed tomography scanning. Blood and fluid aspirate cultures confirmed a diagnosis of melioidosis, a rare fulminant septicaemia in the UK, but endemic in South-east Asia and tropical Australia. Full recovery followed changing antibiotics to intravenous ceftazidime with no relapse 3 years after acute episode. CONCLUSIONS: Physicians as well as microbiologists should consider melioidosis in anyone presenting with septicaemia and/or resistant DKA, especially if the history includes travel to endemic areas or if the cultures suggest Pseudomonas-like organism. With increasing international travel, it is crucial to remember that good travel history could be life-saving in some cases of septicaemia.

Instrumentation to evaluate neural signal recording properties of micromachined microelectrodes inserted in invertebrate nerve.

The design and characterization of instrumentation for application in evaluating the neural signal recording properties of probe-type microelectrodes, micromachined from silicon, are reported. Key aspects include the close matching of gain and frequency response between channels (better than 1%), flexibility in signal conditioning options, the ability to operate with a wide range of (microelectrode) recording site dimensions (4 microm x 4 micrm to 50 microm x 50 microm), and hence impedances, and the facility to monitor and store instrumentation settings on computer along with the recorded signals. Noise levels ranged from 3.7 microV rms for a 50 microm site, to 11.7 microV rms for a microm site, measured in saline. Close matching between channels was required to enable comparisons between different sites and different probes to be made with confidence; however, the instrumentation could be readily applied to less demanding applications.

Silicon-based microelectrodes for neurophysiology, micromachined from silicon-on-insulator wafers.

A process is described for the fabrication of silicon-based microelectrodes for neurophysiology using bonded and etched-back silicon-on-insulator (BESOI) wafers. The probe shapes are defined without high levels of boron doping in the silicon; this is considered as a step towards producing probes with active electronics integrated directly beneath the electrodes. Gold electrodes, of 4 microns by 4 microns to 50 microns by 50 microns are fabricated on shanks (cantilever beams) 6 microns thick and which taper to an area approximately 100 microns wide and 200 microns long, which are inserted into the tissue under investigation. The passive probes fabricated have been successfully employed to make acute recordings from locust peripheral nerve.

The development of a long, dual-platform triaxial walkway for the measurement of forces and temporal-spatial data in the clinical assessment of gait.

Force-plate measurement of the ground reaction force (GRF) has, for many years, been considered a vital component of the comprehensive assessment of human gait in the clinical context. For example, the data can be used in the adjustment of prostheses and orthoses and in identifying the mechanisms underlying a gait dysfunction. However, commercial force plates are usually only capable of measuring GRF data from one step in a single traverse. That can lead to problems of 'targeting' and, with less able subjects, fatigue before the necessary data have been collected. Previous work at the University of Surrey resulted in a prototype dual-platform force walkway capable of measuring the vertical component of the GRF and estimating the position of application of that force for multiple foot contacts in a single traverse. In addition, temporal-spatial information, e.g. speed and step length, could also be determined. This paper describes the development of a longer walkway that can measure the three orthogonal components of the GRF and provide and a more accurate estimate of the position of application of that force. Software to allow the rapid reduction of gait data to useful clinical information has also been developed.

Long pulse biphasic electrical stimulation of denervated muscle.

In recent years a number of studies have employed long pulse biphasic stimulation as a treatment for denervated muscle to improve tissue quality and in some cases to improve contractile capability sufficient to restore function. However, in the U.K., this treatment is yet to be widely adopted clinically. A 5 subject, case based pilot study of long pulse biphasic direct stimulation of peripheral limb denervated muscle is being conducted and its effect on the tissue evaluated by measurement of muscle bulk, limb blood flow, and skin temperature. In cases of partial denervation. trapezoidal shaped pulses are used to minimize sensory and motor nerve fiber recruitment.

Comparative analysis of power-line interference between two- or three-electrode biopotential amplifiers.

Differential input amplifiers are commonly used in the measurement of biopotential signals. This is because of their ability to reject common-mode signals, for example power-line interference. Rejection is further enhanced by referencing the subject to the instrumentation system. One such referencing technique uses a third subject electrode connected either to circuit common or to ground. However, these techniques are rarely explained or quantified in the literature. Four recording configurations are examined, isolated and non-isolated amplifiers with two and with three electrodes, and existing models are extended. From a brief assessment of power-line interference sources, it is concluded that only displacement currents induced into the leads and the body need be considered. The effect of these on the four configurations is analysed using SPICE. Results show that interference from displacement currents induced into the leads and into the body is dependent upon the recording configuration used and is significantly lower in three-electrode than in two-electrode amplifiers. Isolation also reduces levels of interference. It is concluded that the choice of referencing may affect interference levels on the biopotential signal significantly. Experimental and further analytical work is planned to confirm this.

Susceptibility to autoimmune thyroiditis in Down's syndrome is associated with the major histocompatibility class II DQA 0301 allele.

OBJECTIVE: Abnormalities of immune function, including thyroid autoimmunity, are common features of Down's syndrome, and the genetic associations of autoimmune thyroiditis have been extensively studied in otherwise normal patients with thyroid disease. In this study we have examined the HLA associations of autoimmune thyroid diseases in a cohort of adult subjects with Down's syndrome, to see whether they differed from those found in other populations. DESIGN AND MEASUREMENTS: Restriction fragment length polymorphism analysis was carried out in 41 subjects whose thyroid status was assessed by measuring thyroid function and autoantibody titres. The genotypes of subjects with and without hypothyroid autoimmune diseases were compared. SUBJECTS: Forty-one older subjects with Down's syndrome and an average age of 46.6 years under review by the Maudsley Hospital. RESULTS: Hypothyroid autoimmune disease in this study group was clearly associated with a 5.5-kb Taq1 DQA restriction fragment length polymorphism (Pc = 0.013) corresponding to the major histocompatibility (MHC) class II DQA 0301 allele. CONCLUSIONS: In contrast to Hashimoto's thyroiditis and atrophic thyroiditis, there is a strong association between class II genotypes and hypothyroid autoimmune disease in Down's syndrome. This implies a role for a gene or genes on chromosome 21 in the development of autoimmune thyroid disease.

Alternative medicine: potential dangers for the diabetic foot.

Two patients with non-insulin-dependent diabetes mellitus and previously undiagnosed peripheral neuropathy consulted separate practitioners in alternative medicine with symptoms of painful cold feet. They both received the traditional Chinese therapy of moxibustion and subsequently developed painless ulceration at the sites of treatment on the feet and legs. These cases re-emphasize the dangers of trauma to the neuropathic limb in patients with diabetes.

Limb blood flow, cardiac output and quadriceps muscle bulk following spinal cord injury and the effect of training for the Odstock functional electrical stimulation standing system.

As part of the assessment of the Odstock functional electrical stimulation (FES) standing system for mid to low thoracic lesion spinal cord injured (SCI) subjects, cardiac output, high blood flow and quadriceps muscle thickness were measured before and following an electrical stimulation muscle retraining programme. The same parameters were also measured in a group of uninjured subjects and in SCI subjects. It was found that there was no difference in cardiac output between the groups. However thigh blood flow was found to be around 65% of normal values in the spinally injured group. This returned to normal values following the retraining programme. The quadriceps muscle wasted to approximately 50% of its original thickness in the first 3 weeks following spinal cord injury. The retraining programme increased the muscle thickness to near normal values.

Antigen-specific T cell recognition of affinity-purified and recombinant thyroid peroxidase in autoimmune thyroid disease.

The T cell proliferative responses of peripheral blood lymphocytes from 20 patients with autoimmune thyroid disease (AITD) and 20 healthy controls were analysed to immunoaffinity-purified thyroid peroxidase (TPO) and recombinant antigen preparations generated in Escherichia coli as glutathione-s-transferase fusion proteins. The epitope specificity of the T cell response was investigated using a selection of eight discrete recombinant fragments encompassing the whole of the extracellular region of the TPO molecule. Significant differences in the proliferative responses between patients and controls were observed to the full length, affinity-purified TPO molecule (P less than 0.002) as well as to the recombinant fragments R1c (residues 145-250) (P less than 0.001) and R2b (residues 457-589) (P less than 0.001) suggesting the presence of at least two distinct T cell determinants on this autoantigen. One of these T cell epitopes, localized within the region R1c, has not previously been identified by studies with synthetic peptides.

Assessment of gall bladder dynamics, cholecystokinin release and the development of gallstones during octreotide therapy for acromegaly.

The development of gallstones is a well recognized complication of therapy with the long-acting somatostatin analogue, octreotide in patients with acromegaly. A group of nine acromegalic patients was treated with octreotide at doses of 300-600 micrograms daily for 8 months and the changes in fasting and post-prandial cholecystokinin release, and gall bladder motor function (determined by a radiosotopic technique) were assessed at regular intervals. In addition the development of any gallstones was determined by serial ultrasonography. Fasting cholecystokinin levels showed no significant change over 6 months, whereas the post-prandial levels demonstrated a significant decrease (p less than 0.01) during therapy, yet remained significantly higher than fasting levels. Twenty-four hours after commencing therapy gall bladder ejection fraction was decreased by 57 +/- 23 per cent and gall bladder ejection rate decreased by 63 +/- 19 per cent compared to the pretreatment values, whereas after 6 months' therapy a marked reduction in gall bladder ejection fraction (greater than 35 per cent) and gall bladder ejection rate (greater than 40 per cent) persisted in only four of nine patients. Three of these four patients with persistently impaired gall bladder motor function were subsequently shown to have developed either gallstones or biliary sludge during the course of therapy. We conclude that treatment with octreotide is associated with an impaired post-prandial release of cholecystokinin in all acromegalic patients, but gallstones only develop in those patients who, in addition, have evidence of a persistently impaired gall bladder motor response to cholecystokinin.